Automatic telephone exchange system



June 2, 1931. w. w. CARPENTER 1,308,527

AUTOMATIC TELEPHONE EXCHANGE SYSTEM Filed Jan. 6. 1930 11 Sheets-Sheet l F/a./ [7615/7616 fla H612 F7523 H527 Hay ff-KWIIHII W W GA RPENTER @aaww A TTUHNEY June 2, 1931. w. w. CARPENTER AUTOMATIC TELEPHONE EXCHANGE SYSTEM Filed Jan. 6. 1930 11 Sheets-Sheet 2 IHI- ATTORNEY June 2, 1931- w. w. CARPENTER A ,8 ,5 7

AUTOMATIC TELEPHONE EXCHANGE SYSTEM Filed Jan. 6, 1930' 11Sheets-Sheet 3 //VVEN7'0R W W GA RPENTE/i', 5y d June 2,- 1931. w, w, QARPENTER 1,808,527

AUTOMATIC TELEPHONE EXCHANGE SYSTlll Filed Jan. 6i 193Q 11 Sheets-Sheet 4 rowwm 05 i E. f i a a" 1 E U as T 22 I 3% m I r I lNl/E/VTUR W W CARPENTER BY 461114 A TTOH/VE Y Faun/2E0 June 2, 1931. w. w. CARPENTER 1,808,527

I AUTOMATIC TELEPHONE EXCHANGE SYSTEM File d Jan. 6. 1930 11 Sheets-Sheet 5 //v VEN TUE W W GA RPENTER A 7' TO/TWE Y June 2, 1931.

Fla. 6.

w. w. CARPENTER 1,808,527

AUTOMATIC TELEPHONE EXCHANGE SYSTEM Filed Jan. 6, 1930 11 Sheets-Sheet 6 //vv/vr0/? M4 W CARPENTER A TTUHNEY.

June 2, 1931. w, w, QARPENTER 1,808,527

AUTOMATIC TELEPHONE EXCHANGE SYSTEM Filed'Jan..6, 1930 11 Sheets-Sheet 7 may" lNl/E/VTDR W W UA/FPENTE'R A TmR/VEY June 1931- w. w. CARENTER v AUTQMATIC TELEPHONE EXCHANGE SYSTEM Filed Jan. 6, 1930 11 Sheets-Sheet 8 MARGINAL M/VE/Qm/i W W CARPENTER BY $6.6M

June 2, 1931. w. w. CARPENTER AUTOMATIC TELEPHONE EXCHANGE SY STEM Filed Jan. 6, 1950 11 Sheets-Sheet 9 //Vl EN TOR. W W CARPENTER BY 6 c/mifl- ESQ A TTOFINE) JunZ, 1931. I W. W.CARPENTE R AUTOMATIC TELEPHONE EXCHANGE SYSTEM Filed Jan. s, 1930' '11' Sheets-Sheet 1o 560 I H6. 0. m5 /025 //Vl/E/V70/? W W CARPENTER BY 62 6. Jaw- A TTO/FWEY June 2, 1931. w. w. CARPENTER AUTOMATIC TELEPHONE EXCHANGE SXSSTEM Filed Jan. 6, 1930 1 1 Sheets-Sheet ll Patented June 2, 1931 t UNITED stares P m WARREN w. CARPENTER, or QUEEN$ VILLAGE, NEW YORK, As sIenon ronnrm TELE- PHONE LABORATORIES, INCORPORATED, on NEW YORK, 1v. Y., A'ICORPQRATION or N YORK AUTOMATIC TELEPHONE EXCHANGE SYSTEM Application filed il'anuary 6,1930. Serial No. $18,878.

most cities, these lines are divided amonga number of otfices which together form what is known as an exchange area. The number of oflices, of course, is determined by the geographical distribution of the subscribers to be served and by thedensity of the telephone development in a given section.

It generally occurs thatcertain of theseoffices will serve lines which are used almost exclusively for business purposes and others will serve lines which are .used for a variety of purposes other than those classed as strictly business. In oflices where business lines predominate the peak load isduring ordinary business hours and after such hours the load may drop off to practically nothing whereas in the residential districts the peak load is often after business hours. There may be other local conditions which would cause the peak load in the various offices to occur-at difierent times during the day. l or example, reference may be madeto the situation in New York city where ofiices' serving the financial district in the lower part of the city are practically without load after 5 oclock whereas the peak load in an ofiice serving the hotel and theatrical'district occurs between 7 and 8 oclock in the evening.

It is the usual practice in offices which are worked on. an automatic basis to provide sufficient equipment in the way of line finders, selectors, and control equipment to take care of the peak load. A certain portion ofthis p 131011 a switching arrangement is provided at equipment is idle when the load is at its minimum.- Apparatus which is idle is not worked at a maximum efficiencyrand fixed charges-and depreciation are present whether the equipment is operating or not. v

In accordance with the present invention advantage is taken of the fact that the peak loads in one or more oliices are at different Y trict.

inte rofiice "trunks Eto the hours of the day and makes equipment in certainolfices during this period'oit light load available for handling calls incomingto an oiiice operating at a peak load. As a result it is not necessary to install in theotlice which is to be assisted, equipment necessary to handle its peak-load. These economies .are effected both'inthe initial amount of equipment installed andin the moreeflicient use of the equipment that is installed. 1

, More specifically in accordance with the invention it is proposed to automatically connectline findersinone olfice with selector switches and control apparatus of another oflice by means of trunkconductors normally .New York city wherein theHanover ofiice serves the financial district and "the Pennsylvania oflice serves thehotel andftheatre dis- In accordance with-the invention the line finders at the Pennsylvania ofiice serving incoming calls therea't'are not all: connected to district selectors but are -,cb!inected by Those calls incoming. at the Pennsylvania 5 used for handling calls between the oflices. I

Hanover ofiice.

oiiice which normally would'be handled by the line finders and paired'district selector switches of the Pennsylvan a ofiice .areautomatically routed over the interoficeftrunks to the Hanover ofiice and handled through district selectors andcontrol equipment of-the .Hanover ofiice at such timesas a peak load arises at'the Pennsylvania oflice. .By utilizing selector switches andcontrol apparatus at the Hanover. otfice theapeak load at the Pennsylvania oifice may be cared .for without the addition of a large' amoun-t ofequipment which otherwise would be' used only during periods ofheavy traflic. a

In accordance with a feature of the invenone ofiice which is to beu sed for'receiving overflow calls from a certain ofiice for disassociating-certain district selectors from their normal connection with line'finders andpairing such district selectorsover the interofii'ce trunks with the auxiliary line finders 'o fthe oflice from which the foyer-flow load is to be gether with common tor, the district selector being received. The same switching arrangement also segregates a portion of the link circuits employed for associating idle line finder district links with idle senders and renders such segregated link circuits available only for as sociating the auxiliary line finders of one office with the idle senders of the other ofiice.

pose of the invention may. be obtained from a consideration of the following description inconnection with the attached drawings in which Figs. 1 to '5 show apparatus at an oifice A of an exchange system; and,

Figs. 6 to 10 show apparatus at anofice B of the same exchange; 7

Fig. 1 shows a calling subscribers line together with relay equipment common to a group of lines;

F' g. 2 shows a start circuit; 7 r

Fig. 3 shows aline finder and district selector; r Fig. 4 shows alink circuit for associating asender, diagrammatically illustrated, with "i so thedistrict selector of Fig. 3

Fig. 5 shows a line finder having access to the calling line for serving such calling line during periods of peak load and associable with a district selector, Fig. 8, of ofiice B;

Fig. 6 shows a calling subscribers line torelay equipment terminating inofiice B; j

Fig. 7 shows a start circuit. v V

Fig.8 shows a line finder and district selecarranged to be paired with the line finder of Fig. 5, and in .the'lower right portion a representation of a line finder-district which may be used only for calls locally originated. f

Figs. 9 and 10 show link circuits for associating v senders, diagrammatically illustrated with the district selectors of Fig. 8;

Fig. 11 is adiagram showing howthe several figures should be arranged to illustrate the complete circuits of the-invention; and

' Fig. 12 is "a schematic drawing illustrating the principles of the invention.

I The invention has been embodied in a disclosure which is substantially like that of Patent No. 1,690,206 granted to'A. Raynsford, November 6,1928. The senders'diagrammatically indicated by the smallrectangles in the upper left corner of Figs. 4, 9 and-10 are of the character disclosed in the Patent No. 1,589,402 granted to O. HaKopp, J une22, 1926, and reference to the Kopp patent is made for operations not completely described herein. 1 g

As in the disclosures of the above mentioned patents, aplurality'of link circuits is associate the line finder of Fig.

provided at each exchange oflice arranged to serve a group of calling lines and are taken into service in rotation. When a link circuit completes its function it hunts for and associates itself with a district selector is ready for use and the link and district remain in a suballotted condition until the next link in the series has been put into service.

' The link circuit is then put into an allotted position from which it will be advanced by the initiation of a call and the action of the associated start circuit. For example, the trip circuit of Fig. 1 and start circuit of Fig. 2 are so arranged that only one line of a group of lines may be served at a time and so that there may be cooperation between two sub-groups of lines to each of which the group of link circuits of Fig. 4: is individual. The details of these functions form no particular part of the present invention and are fully described in Patent No. 1,567,072 granted to W. H. Matthies, December 29,1925.

The start circuit of Fig. 2, however, differs from the start circuits of the above mentioned patents in that provision is made for starting a link circuit of an ofiice B in which at thetime trafiic is light, in the event that at the time when a call is initiated in either of the line sub-groups of Fig. 1 the traffic is so heavy that there areno links and senders available in oflice A for serving the call. At such periods of peak load the keys shown in the lower right portion of the start circuit of-Fig. 2 positions I right portion of Fig. 5 will be operated to 5 with an interoffice trunk extending to a district selector in office B. When such a condition arises a call is transferred to the start circuitof Fig. 7, and a preallotted'link, Fig. 10, of

office B is started to select a sender and to associate it with a district selector of office B for serving the call.

In addition, the start, link and district 1' selectors of office B shown in Figs. 7, 9 and 8 are modified by the addition. of keys which enable this apparatus'to' bemade available which will be operated to their alternate and the key shown in the upper for serving calls originating in oflice A during periods of light load in oflice B. The '1 keys associated with the district selectorof Fig. 8 are applied 'OIIlY tO ZL portion of'the district selectors of the frame and when operated disassociate such selectors from their normal association with line finders of ofiice B and associate them with special line finders such as shown in Fig. 5 in the same frame as the line finder of Fig; 3 serving the group of calling lines shown in Fig. 1 of Referring particularly to Fig. 12 in which apparatus of two offices A and B of an exchange system have been schematically illustrated, it will be assumed that oflice A is an oifice in which a peak load may occur at a above mentioned patent-s.

time when the load in oflice B is light. In

oflice A the linefinders300 servingthe group of'subscribers lines are shown paired'with district selectors 350, the line finders in the "left half of the line finder frame being an ranged to be started through the start circuit 250 and a preallotted link of the A group of link circuits 1200 and the line finders in the right'half of the frame being. arranged to be started by a link inthe B group 1201 in accordance with the practiceset forth in the In accordance with this invention each half of the line finder frame is also equipped with certain line finders which are linked over interofiice trunks of the trunk group 555 with certain district selectors 890 in the district selector line finders of the left half of the line finder frame are arranged to] be startedthrough the start circuit (50 and a preallotted link of the A group of link circuits, and the line finders of the right half of the frame are arranged to be started through the start circuit 750 and a preallotted link of the B group of link circuits. During such normal load periods with the keys illustratedin their normal positions, all of the apparatus of office B is effective only for handling calls originating in such o-ifice.

When, howeven avperiod of light load occurs in the oflice B and a period of peak load occurs atthe same time' in the A office, the attendant at office B'by operating the keys indicated may render the districtselectors 890 available for pairing with the line finders 550 of ofiice A over trunks 555 and mayt'ransfer the start leads of half of the link circuits of both A and B groups from their normal connection with the start circuit 750 to the start circuit of ofiice vA over trunks 983 and 1204. If then, all of the apparatus of office A available for serving the group of lines illustrated becomes busy, the transfer relay 230 operates transferring the start conductors extending from start circuit v250 from the link start conductors 229 and 1203 extending to the A and'B- groups of links in otfice A to conductors-983 and 1204 extending to the A and B groups of links in ofiice B. Thus on such peak load calls initiated in office A the links of office B will function to select an idle sender and associate it with an allotted district selector in ofice B to serve such calls. i

Calls originating ca of ice Aumd served by apparatus in 0777306 B Since underconditions of normal load the apparatus of ofiice A functions in the well- -know n1m'anner-, fully set forth in the patents referred to, it will not be necessary to describe herein in detail the manner in whicha call'is extended under those conditions. It.

will therefore be assumed that at the time the subscriber-of calling station 100 initiates a call the links and senders which wouldordinarily be available for use are busy because of a peak load condition and that duringthe existence of that condition the keys 221, 222, 223 and 224 are operated. With these keys opera'ted -and all ofthe link circuits of both the A and B groups busy, circuits are established for the relays 225 and 226. The circuit of relay-226 may betraced from battery, through the winding of relay 226, the upper alternatecontacts of key 222, conductor 229, sequence switch contacts 424, 454 and 453 of busy link circuits of the A group to ground. A similar circuit will also; be effective for relay 225 over sequence switch contacts of the busy link circuits of the B group.-

When the subscriber at substation 100 removes his receiver from the switchhook acircuit is closed from battery, through the winding of line relay 101, inner back Contact of relay 102, over the subscribers line to i ground at the outer contact of relay 102. R'elay 101 in operating closes a circuit from battery, through resistance 104, winding of relay 103 to ground at the rightco-ntact of relay 101. It also prepares a circuit from battery, throughresistance l-lland the right 'winding of relay 109 in parallel, left front contact of relay 101 torconductor 114:to identify the calling line to-the line finders having access to that line. Relay .103 in operating closes a circuit from battery, over the back contact of relay 201, conductor 130, right winding of relay 108, outer right back contact of relay 107, inner right contact of relay 103 to ground at the outer contact of relay 109.

Relay 108 operates in this circuit and front contact, through the winding of trip magnets 303 and 5030f the line finders of the frame serving the sub-group of lines in which the substation 100 is located to battery in preparation for tripping the proper set of brushes of the line finder. In actual practice but one trip magnet such as 303 would be used for a single brush group of allline finders of thesame frame. However, for the sake of clarity a separate trip magnet has Relayf been illustrated for each line finder. 201 operates. in the locking circuit of relay 108,-and in combination therewith closes a relay 108, winding of relay 110 to battery.

Relay-110 looks over its right" contact to ground at the outer back contact of relay 109 and closes a circuit for starting an allotted line finder. r i v i It has been assumed that there areno idle link circuits available in office A and that an idle link circuit, for example, link circuit 1099 of Fig. 10, office B is to be used. The sequence switch 1000 of this link circuit will therefore be standing in position land the sequence switch 800 of the district selector, Fig. 8, preallotted by the link circuit of Fig. 10 will be standing in position 2. At this time since all of the links of oflice A normally available for serving the group of lines in which the calling line is located are busy, relays 225 and 226 are operated thereby establishing an obvious circuit for relay 230. The operation of relay110 will therefore close a circuit from ground at its left contact, the outer left contact of relay 108, the inner left contact of relay 103, conductor 131, left back contact of relay 202, inner left back contact of relay 203, theright front contact of relay 230, conductor 231, alternate contact of key 982, conductor 983, lower contacts of cam 1003, brush-1002, terminal 1001, conductor 87 8, the lower left and upper right contacts of cam 801, winding of relay 802, to

battery. Relay 230 locks over its right 1 Winding and right contact in this circuit to prevent the opening of the start circuit should I a link in office A become available at this time and release either relay 225 or 226.. Relay 802 in operating closes a circuit from battery through the winding of relay 808, al-

ternate contact of, key 805, inner right contact of relay 802, right contact of cam 806, outer left front contact of relay 802 to ground at the lower right contact of cam 807. It has been assumed that the keys of all line finderdistrict circuits of. the frame on whichthe line finder-districts shown in Fig. 8 are located have all been operated to their alternate positions for handling peak load calls originating in office A. Relay 808: upon operating establishes a circuit extending over the conductors and 505 of the interoifice trunk normally used for extending calls fromthe bank of a district selector in office A to an incoming selector in office B,.butset apartfor. peak load calls through the operation ofkey 809 at office B and .key 506 .atoliice B, for

operating relay 501 associated-with the line finder, Fig. 5, of oliice A. This circuit may be traced from battery, through the winding of relay 501, the lower normal'contact of relay 507, the low-er alternate contacts of key 506, conductor 504, the lower alternatecontacts of key 809, the inner normal contacts of relay 810, the upper back contact of relay 811, winding of relay812, the innerupper contact of relay 808, the upper back contact of relay 811, the outer normal contacts of relay 810, the upper alternate contacts of key 809, conductor 505, the upper alternate contacts of key 506 to ground at the upper normal contacts of relay 507. Relays 501' and "812 operate in this circuit, relay 501 closing Relay 514: being shunted by ground at the contact of relay 500 doesnot operate in this locking circuit as long. as relay 500- remains energized. The line finder of Fig. 5 moves upwardlyunder control-of magnet 512 and since trip magnet 503 is operated the proper set of brushes is tripped. 7

As soon as the line finder leaves normal, :1. locking circuit is provided for relay 500 extending from battery through the left contact of relay 500, the back'contact of relay 516, commutator strip 517, brush 518 to ground over brush 510, strip 511 and the right contact of relay 501 which holds relay 500 operated. As soon as the commutator brush 519 engages segment 520 a circuit is closed fromground over" brushes 510 and 519, segment 520, conductor 404, contact 232 of key 20 1, inner front contact of'relay 201 to conductor 129 and the right Winding of relay 201.- This circuitshunts the left winding of .relay. 108 and causes that-relay-to release in turn releasing the trip magnet 503. When brush 519 leaves segment 520 the circuit of relay 201 is opened. and that relay releases freeing thestart circuit of Fig. 2 and releasing relay 802 in the district selector of Fig. 8. When the line'finder brush 521 makes contact with terminal 522 which is connected to conductor 114 and therefore to battery minals of the calling line, a second holding circuitextending from battery, through the winding and left contact of relay,500, over centering strip 523, brushes 509. and 510 to ground, is opened at an insulating segment of strip 523 and relay 500 releases opening the circuit of up-drive magnet 512 and removing the shunt ground from the winding of relay 514 which now operates in the locking circuit of relay 513. Relay 51% upon operating opens the circuit of relays 516 and 109, at its outer right contact establishes an obvious. circuit for relay 507, itsinner right contact, es

tablishes a circuit for the cut-oif relay 102 of the calling line extending frombattery, through the windings of relay 102, conductor 112,- terminal 52'and brush 525 to ground,

and at its left frontcontact connects direct ground to brush 521 ..over the right normal contacts of relay 526, tlic right front coniact of relay 502, commutator strip 517, brushes 518 and 510, strip 511 toground at the right front contact of relay 501 and after relay 507- operates, to ground atthe lower front contact ofj-re-lay 507. Relay 109 which operated in series with relay '516 opens the holding circuit of relay 110 thereby restoring the relay 0 equipment of Fig. 1 so that another calling line in the same line group may have access to the common start circuit for starting. an-

other call. Relay 507 upon operating discon nects ground and the .winding'jof relay501 from the trunk conductors 505 and 50-1 andv extends these trunk conductors through the windings of relays 527 and 528 over brushes 529 and 530 and terminals 581 and 532 to the conductors .of the calling line. Relay 812 in-the district circuit of Fig. 8 is maintained energized overthe calling line loop due to thetransfer contacts of relay 507v and relay 527 operates in series therewith. Relay 528 beingpolarized does not receive current n the right direction through its windings to operate at this time. Relay 527 upon, opertit ingclosesat its contacts new'operating circuit for relay 502for replacing theoriginal circuit opened at the contacts of relay 501' upon therelease of that relay.

At the district selecto'rof Fig. 8 upon the' operation of relay 812. a circuit is closed extending from ground at the contacts of relay 812, over the lower back contact of relay 811 to battery through the winding of relay 13. Relav 813 operates locking over its front con- 4 vi 1 1 uact, through the winding or 1e ay 811 to ground at the upper front contact of relay 808, but relay 811 being shunted as long as relay .812 remains operated does not operate at this time. As soon as relay 802 releases.

following the finding of the calling line as previously described, a circuit is established;

for relay870 extending from battery, wind in of rela 870 contacts ofke 871 resistb y 7 y 7 ating ground for the circuit of relay 811.

Bela 811 thereupon operates openin the initial operating circuit of relay 813 and transferring'the trunk conductors 505 and j 504 fr'om-fl their connection with-thewinding of relay 812, over back contacts of relay 8 141 tocams 815 and 816. I

-Atthe time relay'802 operated it closed a circuit from ground atv the lower rightcontact of cam 807, over the outer left front contact ofrelay 802,1ower left contact cream 817, conductor S18,terminal 1007, brush 1006 of the link dis lot finder 1010, upper right contactlof cam 1008, winding of relay 1009 resistance 1011 to battery. Belay 1009 operates and closes a circuit from battery,

, through the winding of sequence switch magk net 1000, upper contact of cam 1012 toground at the outer right frontfc'ontact of relay 1009 advancing link sequence. switch 1000to position .l/ v hen sequence switch1000fleayes position l relay 1009 releases, In' position.

2a circuit-is closedlfrom battery, through thewinding of relay 1013, right contacts of cam 1014,1eft back contact of relay 1015 to ground at the lower left contact of 0211111010 Relay 1013 operates closing a' circuit from I battery, through the right winding of relay 1017, the outer right contact of relay 1013 to ground at the right back contact of relay 1015. Relay 1017 in operating: closes a circuit. from battery, through the Winding of up-drive magnet 1018 of the sender find-er.

1020, left contact/of cam 1079,. outer right contact'of relay 1017 to ground at the right back contactof relay 1009.' The sender finder moves upwardly under the control of magnet 1018 in'search of an idle sender. p

Relay 1013 also closes a circuit from battery through the middle winding. of relay 1015, upper contacts of cam 1021, right winding of relay 1015 to ground at theinner. right contact of relay 1013., The current in thiscircuit,however, is not sufficient to operate relay 1015 but does create a flux in the windings of that relay so that it becomes quickto operate when the test circuit isclosed. The; test circuit extends from brush 1022,-upper contacts of cam-1019, left back co-ntactof re} lay 1009, left winding of relay 1015, 1 lower r ght and upper left contacts of cam 1021, right winding of relay 1015 to ground at the inner rightcontact of. relay 1013. An idlesender is characterized by battery'potential on terminal 1023 and therefore when brush 1022 engages terminal 10:23am above tracedcircuit is completed and relay1015 operates quickly closing'a'lockingcircuit for itself trom battery, through its middle winding,

theupper. contactsof cam 1021, its right front contactto ground. It also opens thecircuit of relay 1017 which releases to: inturn release,

magnet 1018 and bring the sender finder 1020 to rest on the terminals of the idle sender The releasev of relay 1017 in-turn releases re lay1013. Vilith relay1013 releasedland relay1015 operated a circuit is closed from battery, through the winding of sequence switch magnet 11000, upper left-contact of cam'1076, i"

contacts 1027' of j ad: 1028, left, bachfconta'ct of relay 1013, left front contact of relay 1015 to ground at the left lower contact of cam 1016 thus advancing sequence switch 1000 to position 3.

I 'As soon as sequence switch 1000 reached position 1% a circuit was established from ground, over the right contact of cam 1029, brush 1078, terminal 1077, conductor 822, the lower left contact of cam 823, the lower left contact of cam 824, to battery through the left winding of relay825. Relay 825 upon operating with relay 802 released, closes a circuit for advancing sequence switch 800 into position 3. This circuit extends from battery, through the winding of sequence switch magnet 800, the upper right contact of cam 826, the inner right contact of relay 825,

the outer left back contact of relay 822 to ground at the lower right contact of cam 807.

"With sequence switch 800 in position 3, relay 870 is held operated over key 871, resistance 872, the innermost lower back contact of relay 814 to ground at the lower contact of cam 833.

'When sequence switch 1000. reaches position 3 a circuit is closed from ground at the sender over terminal 1030, brush 1031, the

lower contact of cam 1034, brush 1032, terminal 1033, conductor 819, lower right and upper left contacts of cam 820 to battery through the upper winding of relay 814 and 1 in parallel therewith over the upper rightcontact of cam 820, throughthe winding of relay 821 to battery. Relay 814 is marginal and does not operate, but relay 821 operates although ineffective at this time,

As soon as sequence switch 1000arrived'in position 2 it prepared thepulsing circuit for receiving dlalingimpulses. Thls circuit may be traced from the sender, over terminal 1040, brush 1041, the lower contact of cam 1029, brush 1078, terminal 1077, conductor 822, the upper left contact of cam815, the

upper'contact of relay 814, thence as traced over the calling subscribers line loop returnmg tact of relay 814, the winding of-supervisory relay 827, the'left contact of cam 816, concductor 828, terminal 1042, brush 1043, the

over the intermediate lower back conupper contacts of cam 1003, brush 1044,

terminal 1045 to the sender. Upon the establishment of the pulsing circuit a dialing toneis transmitted to the calling line inthe well-known manner to inform the calling subscriber that the sender is ready to receive impulses which he may then send out by manipulating his dial. 1

Upon the seizure of the sender battery is removed from terminal 1023, thus releasing relay 1015, which closes a circuit for advancing sequence switch 1000 into position 5.

This circuit maybe traced from battery through the winding of magnet51000, the

upper right contact of cam 1076, the left back contact of relay 1015 to ground at the lower left contactof cam 1016. Sequence switch 1000 remains in position 5 throughout'the further operation of the sender. As soon as the calling subscriber has dialed the office code digits,-the sender establishes a funda mental circuit for controlling the district 825, the lower left contact of cam 824,.upper left contactof cam 823, conductor 878, terminal 1001, brush 1002, theupper contacts of" selector of Fig. 8 which may be traced from? battery'through the left winding of relay cam 1035, brush 1036, terminal 1037, through v the winding of the stepping relay (not shown) of the sender to ground. Relay 825 energizes in this circuit and locks over its outer right front contact and the upper right contact of cam 824 to the fundamental cir 1 cuit and also closes a circuit from battery 1 through the winding of sequence switch magnet 800, upper right contact of cam 826,

inner right front contact of relay 825, outer left back contact of relay 802 to ground at the lower right contactpof cam 807. Magnet.

causes the district selector switch shaft to" i move upwardly in a brush selecting movemakescontact with a'conducting segment of strip 829, a shunt circuit is established from ;ment. Each time the commutator brush 830 groundat the rightcontact of cam 833, over brush 830 and strip 829, the'upperright contact of cam 823, the upper right contact of cam 824, the outer right front contact of relay 825 to the Winding of relay 825 for holding V this relay operated, but shuntingdown the sender stepping relay. In the well-known manner the operation of the sender stepping relay operates'counting relays of the sender until the sender is satisfied as to the district brush selection codedby the office code registers, when the fundamental circuitis opened at the sender thereby permitting relay 825 to release as soon as brush 830 leaves thecon-' ductingsegment of strip 829 upon which it last rested. vThe release of relay .825opens the circuit of the updrive magnet 831 and closes a circuit from battery through the Y winding of sequence switch magnet 800, the

right contacts of cam 834, the inner right switch into position 5.

With sequence switch 800 in position 5, the

' V a fundamentalcircult is again closed as previously traced, whereuponthe stepping relay 3 back contact of relay 825 to ground 'aspreviously traced for advancing the sequence of the sender and relay825 again operate,

relay 825 looking to the fundamental circuit over the circuit previously traced and closing the previously traced circuit for advancing sequence switch 800 intoposition 6. As soon as the sequence switch reaches position 5' a circuit is established for the trip magnet 835' extending from battery through the winding of magnet 835 to ground at the lower right contact of cam 836. With sequence switch 800 in position 6, the circuit for the updrive magnet 831 is again closed over the circuit previously traced and magnet 831 causes the switch shaft to move upwardly in its group selection movement During theinitlal portion of this movement due to the energization' over brush 837, commutator strip 838, the

lower right and upper left contacts of cam 824, the outer right front contact and left winding ofrelay. 825 to battery for holding relay 825 operated and for shunting down the sender stepping relay. Y At the'sender in response to the intermittent operation of the stepping relay, counting relays are operated in the well-known manner'until the sender is satisfied with respectto the district group selection coded by the office code registers when the fundamental circuit will be opened at the sender, permitting the release of relay 825 as soon as brush 837 engages the next insulating portion of strip 838, Relay 825 upon releasing opens-the circuit ofupdrive magnet 831 to arrest the upward movement of the switch shaft with the tripped set of brushes 839, 840 and 841 in engagement with'th'e lowermost group. Relay 825 in releasing also establishes the previously traced circuit for ad? vancingsequence switch 800 into position Z. In position 7 of sequence swltch 800, re, lay 825 is operated in a circuit extending from 1 battery through its right winding, the upper right contact of cam 842, lower right contact of cam 843,'back contactof relay 856, commutator strip 857, brush 858 to ground. Relay 825 energizes in this circuit closing a circuit for advancing sequence switch 800' into position 8. This circuit may be traced from batterythrough the winding ofmagnet 800, upper right contact ofcam 826, inner right front contact of relay 825,.the outer left back contact of relay 802, to ground at,

the lower right contact of cam 807. In'positions 7 ,4 to 8, relay 825 locks over its left contact, the right contacts 'of' cam 845 to the test brush 839 and ground over the sleeve terminal of the trunk provided that trunk is busy. The original energizing circuit of relay 825 is opened when-the sequence switch leaves position 7 .v groupis busy, however, relay 825 is'held en ergizedin position 8 and a circuit is complet If the first trunk of the 7 ed' for the updrive magnet 831 from battery contact ofrelay 825 to groundias traced. The 7 updrive magnet is energized and causes the selector shaft to move upwardly in search'of an idleoutgoing trunk. Relay 825 is held energized as the test brush 839 passes from terminal to terminal over. a circuit extending from battery through the. right winding of relay 825, the right contacts of cam 842, commutator strip 846, brush 847, the upper right and lower left contacts of cam 832, the inner right front Contact of relay 825, thence to ground as traced. As soon as an idle trunk is reached characterized by the absence of.

ground on its sleeve terminal, the locking circuit of relay 825 is'opened and thatlrelay releases, in turn, releasing the updrive mag net 881 to bring the district selector'to rest with its brushes 829, 840 and-841 on the terminals of the selected idle trunk --The release of relay 825 closes acircuit from battery through the windingof sequence switchmagnet 800, the right cont-acts of cami 834, the inner right back contact of relay 825 to ground as traced for. advancing sequence switch 800 into position 9. v I

As soon as relay 825releases ground is connected to sleevebrush839, overv the upper contacts of'cam 848,-the outer right back con-x tact of relay 825 'toground at the upper left': contact of cam 833. As soon as the sequence switch arrivesin position 8% ground is con nected over the lower. right and upper left contacts of cam 848 to sleeve brush'839 independent ofrelay'825 which gr'ound'is maintained until the sequence switch leaves poset 'ofbank terminals in the selected trunk sit-ion 715 A With sequenceswitch' 800 in position 9, clrcult is completed from battery through the right winding of-relay 825, the lower, left contact of cam 844, the right front-contact of tact of cam 826, inner right front contact;

of relay 825 toground as traced foradvancmg sequence switch 800 into position 10, in

which position it remains until all subsequent selections are completed." In this position the fundamental circuit over which subsequent selections are controlled extends from brush 841, over the upper left and lower right contacts of cam 849, the right back contact of relay 850, thenceas traced over conductor 878 to the sender returning over terminal 1039, brush 1088, the upper left and lower right contactsrof cam1005pbrush. 1006, terminal-1007, conductor 818, the lower contacts of cam 851 to-brush840.

Following the completion of units selection and the advance of thefincoming sclector,cu'rrent over the fundamental circuit is reversed and the sender is prepared for making talking selection. At this time the sender increases the resistance in the circuit of relay 821 to such an extent that it releases, opening the circuit of relay-825 which in turn releases, closing a circuit from battery through the. winding of sequence switch magnet 800,. over the right contacts of cam 834, the inner right back contact of relay 825 to ground as traced for advancing sequence switch 800 out of position 10 into position '11. As soon as,

' sequence switch 800 reaches position 11 a circuit is closed for magnet 800 over the upper right contact of cam .826, the lower left and upper right contacts of cam 832, togrouncl at the right contact of cam 833 for advancing sequence switch-800 into position 12.

With sequence switch 800 in position 11, a localcircuit is established for relay 821, extending from battery through the winding of relay 821, the right contacts of cam 820 toground at the lower left contact of cam 836,

and ground is connected to the sender over the lower left contact of cam 836, conductor 819, terminal 1033, brush 1032, upper contacts of cam 1046, left winding of relay 1015, left back contact of relay 1009, the upper right contact of cam 1034, brush 1031, terminal 1030 to battery in the sender for advancing the sender for making talking selections. Relay 1015 does not, however, operate in thiscircuit. At this time the calling line is connected over the lower contact of cam 815, through theleft windings of repeating coil 852, the upper contactof cam 816, through the windingjof supervisory relay 827, thereby operating relay 827 which establishes a holding circuit for relay 821 extending from battery through the winding of relay 821, the front contact of relay 827 to of the sender operate in this circuit, relay 8 25 closing the previously traced circuit. for advancing sequence'switch 800 out of posia tion 12 and locking itself tofthe fundamental circuit over its outer right front contact and the upper right contact of cam 824; Switch" 800 now advances under the control ofrelay 825 and in positions 12%, 13% and 14% con nectsground over the right contacts of cam 848 in shunt ofthe winding of-the sender.

stepping relay. The position in which 'sequence switch 800 comes to rest is determined by the countingrelays of the sender in accordance with the talking selection registra-I I tion set up by the sender code registers.-

When thesender is satisfied for this selection the fundamental circuit is opened thereby releasing relay 825-and stoppingthe sequence switch 800 in the next stopping position. For

the purposes of this description it will be assumed that sequence switch 800' stops in p0 sition 14. In this positionthe right windings of repeating coil 852 are connected over the left contacts of cam 849 and left contacts of cam 851 to the brushes 841 and 840, respectively, in series over the left contacts of cam 845 andthe winding of polarized relay 853,

and thence to the repeating coil in the incoming selector.

The called line is tested by the final selector and i-f-foundidle, ringing current is applied I I from the incoming selector 1n the usual man ner; When the called subscriber answers re lay 853 operates and as soon as interrupter 854 closes its lower-contact it establishes a circuit for relay 802 extending from battery through the; winding of relay 802, the lower contact. of interrupter 854,1 left contacts of cam 842, front contact of relay853to ground a at the upper left contact of cam 807 Relay 802. operatesand looks over its inner left front contact, the lower contact of relay 808, v the upper leftcontact of cam 843, the upper left contact of cam 842, front contact of relay 8537to ground at the-upper left contact of cam 807 The operation of relay 802 prepares a circuit for relay 850 which may be traced from battery. through the winding tact of relay 853 to ground at the upper left contact of cam'807. Relay 8 50, upon operating, locks over'its inner left front contact to of relay 850, upper left contact of cam 806, outer leftffront contact of relay 802, upper contact of interrupter 854 as soon as the interrupter advances to close its upper contact, theleft contacts of cam 842, the front conground at the upper right contact of cam 807, closes a circuit from' battery over its outer left contact, the contact ofkey 855, to

ground through the winding of relay 810 and atits intermediate left contact establishes a newholding circuit for relay 870.

Relay 810,, upon operating, reverses the connection of trunk conductors 504 and505' to battery and ground through the left wind ings of repeating coil 852, thereby causing current to flow over the inter-oificetrunk' through the windings of polarizedrelay 5,28

vinsuch adirection as to operate this relay.

Belay 528, upon operating, closes circuits in parallel for relays 526 and 533. The circuit .of 'relay533 whichis quick operating but slow to release extending from battery, over theleft back contact of relay 526, winding of relay 533, front contact of relay 528, front contact of relay 502, commutator strip517,

brushes 518 and 510, strip 511 to ground at the lower front contact ,of relay 507. The circuit of relay 526 extends from battery through the winding of this relay to the-contacts of relay 528, thence to ground as just traced. Relay 526 being slow to operate does not operate as quickly as relay 533, therebyallowing relay 533 to operate and establish the obvious circuit for slow-to-release relay 534. Relay 534, upon operating, opens at its normal contacts the circuit hereinbefore traced from ground at the lower contact of relay 507, through the winding of the calling line message register 118 to ground. As soon as relay 526 operates it opens at its left back contact the circuit of relay 533, at its inner right front contact closes a locking circuit for itself eX- tending over the front contact of relay 502 to ground at the lower contact of relay 507 and establishes an operating circuit for the mes sage register 118 extending from battery at its left front contact, over the alternate contacts of relay 534, the outer right alternate contacts of relay 526, the left front contact of relay 514, brush 521, terminal 522, the left back contact of relay 101 to ground through the winding of register magnet 118. This circuit is maintained only for the period re- 2 quired for slow-releasing relays 533 and 534 to release. As soon as relay 534releases battery potential is removed from the operating circuit of magnet 118 and ground over the normal contacts of relay 534, the front contact of relay 502, over the circuit previously traced to the lower contact of relay 507 is substituted therefor, thus insuring that the message register will be operated but once. After talking selection is completed the current in the circuit previously traced through the left winding of relay 1015 is increased to such an extent that relay 1015 opcrates and closes acircuit from battery through the right winding of relay 1017, the left contacts of cam 1021 to ground at the right front contact of relay 1015; Relay 1017 closes a circuit from battery through the winding of sequence switch magnet 1000, upper contact of cam 1079, outer right contact of relay 1017 to ground at the right back contact of relay 1009, advancing sequence switch 1000 into position 6. In this position all the'conductors extending to the sender are opened and the sender is completely released. f

As soon as sequence switch 1000 leaves position 5,- relay 1015 releases and in turn releases relayl7 l/Vith relay 1017 released in position 6, a circuit is closed from battery through the winding of sequence switch magnet 1000, lower left contact of cam 1076, left back contact of relay'1017 to ground at the lower left contact of cam 1016 advancing sequence switch 1000 into position 7. If another district is standing in position 1 await ing association with a link a circuitwill be closed from ground'over the lower left contact of cam 836, the lower contacts of cam 820, jackcontacts 868, conductor 860, con- "p3 tacts of jacks1048 and 1049 upper contact of cam 1016, left back contact of relay 1015, right contacts of cam 1014 to battery through the winding of relay 1013. Relay 1013 closes a circuit from battery, through the right winding of relay 1017, outer right front contact of relay 1013 to ground at the right back contact of relay 1015. Relay 1017 in operating closes a circuit for updrive magnet 1047 of the district finder 1010, lower right contact of cams 1079, outer right contact of relay 1017 to ground at the right back contact of relay 1009. The district finder moves upwardly under the co'n'trol of magnet 1047 in search of district which is in condition to be seized. Such a district is identified by battery connected over the right contacts of cam 859, jack contacts 869, conductor 1091 to terminal 1050. Relay 1013, in operating, closes the same circuit through the right and middle windings ofrelay 1015 as it closed in position 2. At this time the test circuit extends to ground at the inner right front contact of relay 1013, through the right winding .of relay 1015, uppegleft and lower right contacts of'cam 1021, left Winding ofrelay 1015, left back contact of relay 1009, upper right and lower left contacts of cam 1019, contact of jack 1049 to brush 1051. Relay 1015 thereupon quickly, operates looking through its middle winding, the upper con.- tacts of cam 1021 to ground at the right front contact of relay 1015, opening the circuit of relay 1017 to release magnet 1047and bring the district finder to rest on the terminals of the district, and at its leftlaack contact opening the circuit of relay 11013 which also releases. Since key 873 of each district of the frame which is not arranged for use with a line finder of office A' is operated, the link 1099 and all other links of the same group 1099-1099 will not be ablev to select such districts since the test terminals corresponding to terminal 1050 will thus be disconnected. With relay 1015 operated and relays 1013 and 1017 released, a circuit is closed from battery, through the winding of sequence switch magnetl000, upper left contact of cam 1076, contact 1027 of jack 1028, left back contact of relay 1013, left front contact ofv relay 1015, upper contact of cam 1016, contacts of jacks 1049 and 1048, conductor 860, jack contact 868, the lower 'contactsof cam 820 to ground at the lower left contact of 021111 836. Se-

quence switch '1000 advances to position 8 in a 1 this circuit.'

Relay 1015 is held operated in position 8 from battery. at the district selector over conductor. 1091 terminal 1050, brush' 1051, contact of jack; 1049,1ower left and upper right contacts ofcam 1019, back contactof relay .1009, left winding of relay 1015, lower right and upper left contacts of cam 1021 to ound at the right frontcontact of relay 1015. With relay .1015 operated a circuit is closed from ground at the lower leftcontact of cam 1016, 

